1. Field of the Invention
The present invention relates to a hand-held power tool.
2. Description of the Prior Art
Hand-held power tools such as drills, cordless screwdrivers, jigsaws, angle grinders, or electric hedge trimmers that are powered by batteries, rechargeable batteries, or a power cord are generally known. Power tools of this kind have electric motors, which, according to the prior art, are operated with a pulse width modulated voltage or, in the case of corded tools, by means of phase-angle control. As schematically depicted in FIG. 1, a pulse width modulated voltage periodically alternates between a high and low voltage value. When the high voltage value is present, the motor is switched on. When the low voltage is present, the motor is switched off. The ratio of the on-time Ton during a period of pulse width modulated voltage to the total time TPWM of a period of pulse width modulated voltage is referred to as the mark/space ratio and determines the effective electrical output supplied by the motor.
One problem when using the pulse width modulation method is the production and emission of harmonics. Because of the periodic switching back and forth between a high and low voltage level and the resulting current changes, harmonics are produced whose frequency is an uneven multiple of the modulation frequency fPWM of the pulse width modulation (FIG. 2). These harmonics are emitted in the form of EMC interference. Excessively powerful EMC interference can negatively affect other electrical devices such as communication systems.